Motion analysis device, motion analysis system, motion analysis method, program, and recording medium

ABSTRACT

A motion analysis device includes: a first specifying unit that specifies a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of an inertial sensor; a second specifying unit that specifies a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and an adjustment unit that adjusts sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.

BACKGROUND

1. Technical Field

The present invention relates to a motion analysis device, a motion analysis system, a motion analysis method, a program, and a recording medium.

2. Related Art

JP-A-2010-82430 discloses that an image is acquired by performing photographing from the rear side in a hitting direction between an address state to the end of a swing and the image is split into at least three regions by a first straight line passing through a shaft axis of a golf club in the address state and a second straight line intersecting the first straight line and passing through the root of an installed tee and the base of the neck of a golfer.

In coaching of a golf swing, indexes such as a shaft plane and a Hogan's plane are used in many cases. The shaft plane is a plane that is formed by the major axis direction of a shaft of a golf club and a target line (for example, a hitting target direction) at the time of address of golf. The Hogan's plane is a plane that is formed by a target line and an imaginary line connecting a periphery of a shoulder (a shoulder, the base of a neck, or the like) of a golfer to the head (or a ball) of a golf club at the time of a golf address. A region interposed between the shaft plane and the Hogan's plane is called a V zone. A trajectory of a golf club enters the V zone, for example, at the time of downswing, straight-based hitting is known to be realized. Accordingly, goodness and badness of a swing can be estimated according to whether a trajectory of a golf club enters the V zone, for example, at the time of downswing.

However, a method of simply presenting a shaft plane and a Hogan's plane to a user has not been proposed until now. For example, in JP-A-2010-82430, the V zone is specified by photographing a golfer in an address state with a camera and drawing a straight line in an image based on an instruction input from a user. In JP-A-2010-82430, there are problems in that, for example, it is difficult to install a camera so that an entire golfer is contained in an image, it is difficult to visually confirm the V zone on an image (it is difficult for a user to decide a position at which a straight line is drawn), and it is difficult to visually confirm whether a trajectory of a golf club in a downswing is included in the V zone.

SUMMARY

An advantage of some aspects of the invention is to support estimation of goodness or badness of a swing more simply than in the related art.

An aspect of the invention is directed to a motion analysis device including: a first specifying unit that specifies a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of an inertial sensor; a second specifying unit that specifies a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and an adjustment unit that adjusts sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.

With this configuration, it is possible for the user to objectively recognize an address posture from the positions and inclinations of the first and second axes, the size of a space between the first and second axes, and the like and to recognize a positional relation between an assumed trajectory of a swing, and the first and second axes. Therefore, the swing can be estimated simply. Further, the position, the posture, the area, or the like of the space between the first and second axes is adjusted according to the predetermined condition. Therefore, even when a way, a habit, a tendency, or the like of the swing of the user is desired to be considered, a swing can be estimated simply and accurately.

The predetermined condition may be a type of swing of the user. The adjustment unit may adjust at least one of the angle of the first axis and the angle of the second axis according to the type of swing.

With this configuration, since the position, the posture, or the like of the space between the first and second axes is adjusted according to the type of swing, the swing can be estimated simply and accurately in consideration of a tendency or the like of the swing according to the type of swing.

The type of swing may be a slice or a hook, when the type of swing is the slice, the adjustment unit may increase at least the angle of the second axis. When the type of swing is the hook, the adjustment unit may decrease at least the angle of the first axis.

With this configuration, the swing can be estimated simply and accurately in consideration of the position or the like of the trajectory of each of a slice-based swing or a hook-based swing.

The predetermined condition may be a skill level of the user. The adjustment unit may adjust the predetermined angle between the first and second axes according to the skill level.

With this configuration, since the position, the posture, the area, or the like of the space between the first and second axes is adjusted according to the skill level, the swing can be estimated simply and accurately in consideration of the tendency or the like of the swing according to the skill level.

The adjustment unit may increase the predetermined angle as the skill level is lower. The adjustment unit may decrease the predetermined angle as the skill level is higher.

With this configuration, the swing can be estimated simply and accurately in consideration of a variation or the like in the trajectory of each swing of a high skill or a low skill.

The first specifying unit may calculate an angle of the shaft relative to the plane using an output of the inertial sensor at the address posture of the user, and may specify the first axis using information regarding a length of the shaft and this angle.

With this configuration, an inclination angle of the shaft of the exercise tool can be calculated using the fact that the inertial sensor detects only the gravity acceleration at the time of stopping of the user, and thus the direction of the first axis can be specified from the inclination angle.

When the hitting direction is a third axis, the first specifying unit may specify a first imaginary plane including the first and third axes and the second specifying unit may specify a second imaginary plane including the second and third axes. Accordingly, the user can objectively recognize the address posture from the positions and inclinations of the first and second imaginary planes, the size of the space between the first and second imaginary planes, or the like and can recognize the positional relation between the assumed trajectory of the swing and the first and second imaginary planes. Therefore, the swing can be estimated simply.

The exercise tool may include a blow surface. The hitting direction may be a direction perpendicular to the blow surface at the address posture of the user.

With this configuration, by supposing that the user stops at a posture at which the hitting direction is perpendicular to the blow surface of the exercise tool, it is possible to specify the hitting direction using an output of the inertial sensor.

The motion analysis device may further include an image generation unit that generates image data including the first and second axes.

With this configuration, the user can objectively and easily recognize the posture at the time of stopping from the positions and inclinations of the first and second axes, the size of the space between the first and second axes, or the like, and can recognize the positional relation between the assumed trajectory of the swing and the first and second axes in the image. Therefore, the swing can be estimated objectively and simply.

The motion analysis device may further include a motion analysis unit that calculates a trajectory of the exercise tool based on a swing of the user. The image generation unit may generate image data including the first axis, the second axis, and the trajectory.

With this configuration, the user can determine, from the image, whether the trajectory of the swing is included between the first and second axes. Therefore, goodness and badness of the swing can be estimated objectively and simply.

Another aspect of the invention is directed to a motion analysis system including: an inertial sensor; a first specifying unit that specifies a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of the inertial sensor; a second specifying unit that specifies a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and an adjustment unit that adjusts sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.

With this configuration, the user can objectively recognize the address posture from the positions and inclinations of the first and second axes, the size of the space between the first and second axes, or the like, and can recognize the positional relation between the assumed trajectory of the swing and the first and second axes. Therefore, the swing can be estimated simply. Further, the position, the posture, the area, or the like of the space between the first and second axes is adjusted according to the predetermined condition. Therefore, even when the way, the habit, the tendency, or the like of the swing of the user is desired to be considered, the swing can be estimated simply and accurately.

The predetermined condition may be a type of swing of the user. The adjustment unit may adjust at least one of the angle of the first axis and the angle of the second axis according to the type of swing.

With this configuration, since the position, the posture, or the like of the space between the first and second axes is adjusted according to the type of swing, the swing can be estimated simply and accurately in consideration of a tendency or the like of the swing according to the type of swing.

The type of swing may be a slice or a hook. When the type of swing is the slice, the adjustment unit may increase at least the angle of the second axis. When the type of swing is the hook, the adjustment unit may decrease at least the angle of the first axis.

With this configuration, the swing can be estimated simply and accurately in consideration of the position or the like of the trajectory of each of a slice-based swing or a hook-based swing.

The predetermined condition may be a skill level of the user. The adjustment unit may adjust the predetermined angle between the first and second axes according to the skill level.

With this configuration, since the position, the posture, the area, or the like of the space between the first and second axes is adjusted according to the skill level, the swing can be estimated simply and accurately in consideration of the tendency or the like of the swing according to the skill level.

Still another aspect of the invention is directed to a motion analysis method including: specifying a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of an inertial sensor; specifying a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and adjusting sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.

With this configuration, the user can objectively recognize the address posture from the positions and inclinations of the first and second axes, the size of the space between the first and second axes, or the like, and can recognize the positional relation between the assumed trajectory of the swing and the first and second axes. Therefore, the swing can be estimated simply. Further, the position, the posture, the area, or the like of the space between the first and second axes is adjusted according to the predetermined condition. Therefore, even when the way, the habit, the tendency, or the like of the swing of the user is desired to be considered, the swing can be estimated simply and accurately.

The predetermined condition may be a type of swing of the user. In the adjusting of the sizes of the angles, at least one of the angle of the first axis and the angle of the second axis may be adjusted according to the type of swing.

With this configuration, since the position, the posture, or the like of the space between the first and second axes is adjusted according to the type of swing, the swing can be estimated simply and accurately in consideration of a tendency or the like of the swing according to the type of swing.

The type of swing may be a slice or a hook. When the type of swing is the slice, at least the angle of the second axis may be increased in the adjusting of the sizes of the angles. When the type of swing is the hook, at least the angle of the first axis may be decreased in the adjusting of the sizes of the angles.

With this configuration, the swing can be estimated simply and accurately in consideration of the position or the like of the trajectory of each of a slice-based swing or a hook-based swing.

The predetermined condition may be a skill level of the user. In the adjusting of the sizes of the angles, the predetermined angle between the first and second axes may be adjusted according to the skill level.

With this configuration, since the position, the posture, the area, or the like of the space between the first and second axes is adjusted according to the skill level, the swing can be estimated simply and accurately in consideration of the tendency or the like of the swing according to the skill level.

Yet another aspect of the invention is directed to a program causing a computer to perform: specifying a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of an inertial sensor; specifying a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and adjusting sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.

With this configuration, the user can objectively recognize the address posture from the positions and inclinations of the first and second axes, the size of the space between the first and second axes, or the like, and can recognize the positional relation between the assumed trajectory of the swing and the first and second axes. Therefore, the swing can be estimated simply. Further, the position, the posture, the area, or the like of the space between the first and second axes is adjusted according to the predetermined condition. Therefore, even when the way, the habit, the tendency, or the like of the swing of the user is desired to be considered, the swing can be estimated simply and accurately.

Still yet another aspect of the invention is directed to a recording medium that records a program causing a computer to perform: specifying a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of an inertial sensor; specifying a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and adjusting sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.

With this configuration, the user can objectively recognize the address posture from the positions and inclinations of the first and second axes, the size of the space between the first and second axes, or the like, and can recognize the positional relation between the assumed trajectory of the swing and the first and second axes. Therefore, the swing can be estimated simply. Further, the position, the posture, the area, or the like of the space between the first and second axes is adjusted according to the predetermined condition. Therefore, even when the way, the habit, the tendency, or the like of the swing of the user is desired to be considered, the swing can be estimated simply and accurately.

Further another aspect of the invention is directed to a motion analysis device including an adjustment unit that adjusts a size of a center angle of a V zone according to a predetermined condition.

The predetermined condition may be a skill level of the user. The adjustment unit may adjust the center angle according to the skill level.

The adjustment unit may increase the center angle as the skill level is lower. The adjustment unit may decrease the center angle as the skill level is higher.

The exercise tool may include a blow surface. The hitting direction may be a direction perpendicular to the blow surface at a address posture of a user.

The motion analysis device may further include an image generation unit that generates image data including the V zone.

The motion analysis device may further include an motion analysis unit that calculates a trajectory of the exercise tool based on a swing of the user. The image generation unit may generate image data including the V zone and the trajectory.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 is a diagram illustrating an overview of a motion analysis system according to an embodiment of the invention.

FIG. 2 is a diagram illustrating examples of a shaft plane and a Hogan's plane.

FIG. 3 is a block diagram illustrating an example of the configuration of a motion analysis system.

FIG. 4 is a flowchart illustrating an example of a motion analysis process.

FIG. 5 is a plan view illustrating a golf club and a sensor unit at the time of stopping of a user when viewed from the negative side of the X axis.

FIG. 6 is a diagram illustrating a cross section obtained by cutting the shaft plane along the YZ plane when viewed from the negative side of the X axis.

FIG. 7 is a diagram illustrating a cross section obtained by cutting the Hogan's plane along the YZ plane when viewed from the negative side of the X axis.

FIG. 8 is a diagram illustrating examples of angular velocities output from the sensor unit.

FIG. 9 is a diagram illustrating an example of a norm of an angular velocity.

FIG. 10 is a diagram illustrating an example of a differential value of the norm of an angular velocity.

FIG. 11 is a diagram illustrating an example of a screen including a shaft plane and a Hogan's plane.

FIG. 12 is a diagram illustrating an example of a screen on which display setting of a V zone is performed.

FIGS. 13A to 13C are diagrams illustrating examples of a procedure and a screen for adjusting the V zone according to a type of swing.

FIGS. 14A and 14B are diagrams illustrating examples of a procedure and a screen for adjusting the V zone according to a skill level.

FIG. 15 is s diagram illustrating examples of a procedure and a screen for setting a center plane.

FIG. 16 is a diagram illustrating example of a procedure and a screen for setting a reference V zone.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the invention will be described with reference to the drawings. Hereinafter, a motion analysis system performing analysis of a golf swing will be described as an example.

FIG. 1 is a diagram illustrating an overview of a motion analysis system according to an embodiment of the invention.

A motion analysis system 1 includes a sensor unit 10 and a motion analysis device 20.

The sensor unit 10 can measure acceleration generated in each axis direction of three axes and an angular velocity generated in each rotation of the three axes as an inertial sensor and is mounted on a golf club 3 which is an exercise tool. For example, the sensor unit 10 is fitted on apart of the shaft of the golf club 3 when one axis among three detection axes (the x axis, the y axis, and the z axis), for example, the y axis, conforms to the major axis direction of the shaft. Preferably, the sensor unit 10 is fitted at a position close to a grip in which a shock at the time of a shot is rarely delivered and a centrifugal force is not applied at the time of a swing. The shaft is a portion of the handle excluding the head of the golf club 3 and also includes the grip.

A user 2 performs a swing motion of hitting a golf ball (not illustrated) in a pre-decided procedure. For example, the user 2 first holds the golf club 3, takes a posture of address so that the major axis of the shaft of the golf club 3 is vertical to a target line (for example, a hitting target direction), and stops for a predetermined time or more (for example, 1 second or more). Next, the user 2 performs a swing motion to hit the golf ball (which is also referred to as a short or a stroke). The posture of address in the present specification includes a posture in a stop state of the user before start of a swing or a posture in a state in which the user shakes an exercise tool (which is also referred to as waggling or the like) before start of a swing. The target line refers to any hitting direction and is decided as, for example, a hitting target direction in the embodiment.

While the user 2 performs the motion to hit the golf ball in the above-described procedure, the sensor unit 10 measures triaxial acceleration and triaxial angular velocities at a predetermined period (for example, 1 ms) and sequentially transmits the measurement data to the motion analysis device 20. The sensor unit 10 may immediately transmit the measurement data, or may store the measurement data in an internal memory and transmit the measurement data at a desired timing such as the end of a swing motion of the user 2. Communication between the sensor unit 10 and the motion analysis device 20 may be wireless communication or wired communication. Alternatively, the sensor unit 10 may store the measurement data in a recording medium such as a memory card which can be detachably mounted and the motion analysis device 20 may read the measurement data from the recording medium.

The motion analysis device 20 analyzes a swing exercise performed with the golf club 3 by the user 2 using the data measured by the sensor unit 10. In particular, in the embodiment, the motion analysis device 20 specifies a shaft plane (which corresponds to a first imaginary plane or a first axis according to the invention) and a Hogan's plane (which corresponds to a second imaginary plane or a second axis according to the invention) at the time of stopping of the user 2 (the time of address) using the data measured by the sensor unit 10. The motion analysis device 20 calculates a trajectory of the golf club 3 at a swing after the user 2 starts the swing motion. The motion analysis device 20 generates image data including the trajectory of the golf club 3, the shaft plane, and the Hogan's plane in the swing of the user 2 and causes a display unit to display an image according to the image data. By displaying the shaft plane and the Hogan's plane, it is possible to recognize a space called a V zone between the shaft plane and the Hogan's plane. The motion analysis device 20 may be, for example, a portable device such as a smartphone or a personal computer (PC). In FIG. 1, the motion analysis device 20 is mounted on the waist of the user 2, but the mounted position is not particularly limited. Further, the motion analysis device 20 may not be mounted on the user 2.

FIG. 2 is a diagram illustrating examples of the shaft plane and the Hogan's plane. In the embodiment, an XYZ coordinate system (global coordinate system) in which a target line indicating a hitting target direction is an X axis, an axis on a horizontal plane vertical to the X axis is a Y axis, and an upward vertical direction (which is an opposite direction to the direction of the gravity acceleration) is a Z axis is defined. In FIG. 2, the X, Y, and Z axes are shown.

A shaft plane 30 at the time of address of the user 2 is an imaginary plane which includes a first line segment 51 serving as a first axis which lies in the major axis direction (longitudinal direction) of the shaft of the golf club 3 and a third line segment 52 serving as a third axis indicating a hitting target direction and has four vertexes T1, T2, S1, and S2. In the embodiment, a position 61 of the head (blow portion) of the golf club 3 is set as the origin O (0, 0, 0) of the XYZ coordinate system. The first line segment 51 is a line segment which connects the position 61 (the origin O) of the head of the golf club 3 to a position 62 of a grip end. The third line segment 52 is a line segment which has T1 and T2 on the X axis as both ends, has a length TL, and centers on the origin O. When the user 2 takes the above-described address posture at the time of the address, the shaft of the golf club 3 is vertical to the target line (the X axis). Therefore, the third line segment 52 is a line segment which is perpendicular to the major axis direction of the shaft of the golf club 3 (which can also be a line segment perpendicular to or intersects the blow surface of the head on which a ball is hit), that is, a line segment perpendicular to the first line segment 51. The shaft plane 30 is specified by calculating the coordinates of the four vertexes T1, T2, S1, and S2 in the XYZ coordinate system. A method of calculating the coordinates of the four vertexes T1, T2, S1, and S2 will be described in detail below.

A Hogan's plane 40 is an imaginary plane which includes the third line segment 52 and a second line segment 53 serving as a second axis and has four vertexes T1, T2, H1, and H2. In the embodiment, for example, the second line segment 53 is a line segment which connects the position 62 (which is an example of a blow position) of the head (which is a blow portion) of the golf club 3 to a predetermined position 63 (which is, for example, the position of the base of the neck or the position of one of the right and left shoulders) on a line segment connecting both shoulders of the user 2 to one another. Here the second line segment 53 may be, for example, a line segment which connects the predetermined position 63 to the position (which is an example of the blow position) of a ball at the time of address. The Hogan's plane 40 is specified by calculating the coordinates of the four vertexes T1, T2, H1, and H2 in the XYZ coordinate system. A method of calculating the coordinates of the four vertexes T1, T2, H1, and H2 will be described in detail below.

FIG. 3 is a block diagram illustrating an example of the configuration of a motion analysis system.

The sensor unit 10 includes a control unit 11, a communication unit 12, an acceleration sensor 13, and an angular velocity sensor 14.

The acceleration sensor 13 measures acceleration generated in each of mutually intersecting (ideally, orthogonal) triaxial directions and outputs digital signals (acceleration data) according to the sizes and directions of the measured triaxial accelerations.

The angular velocity sensor 14 measures an angular velocity generated at axis rotation of mutually intersecting (ideally, orthogonal) triaxial directions and outputs digital signals (angular velocity data) according to the sizes and directions of the measured triaxial angular velocities.

The control unit 11 controls the sensor unit in an integrated manner. The control unit 11 receives the acceleration data and the angular velocity data from the acceleration sensor 13 and the angular velocity sensor 14, appends time information, and stores the acceleration data and the angular velocity data in a storage unit (not illustrated). The control unit 11 generates packet data in conformity to a communication format by appending time information to the stored measurement data (the acceleration data and the angular velocity data) and outputs the packet data to the communication unit 12.

The acceleration sensor 13 and the angular velocity sensor 14 are ideally fitted in the sensor unit 10 so that the three axes of each sensor match the three axes (the x axis, the y axis, and the z axis) of the rectangular coordinate system (sensor coordinate system) defined for the sensor unit 10, but errors of the fitting angles actually occur. Accordingly, the control unit 11 performs a process of converting the acceleration data and the angular velocity data into data of the xyz coordinate system, using correction parameters calculated in advance according to the errors of the fitting angles.

The control unit 11 may perform a temperature correction process of the acceleration sensor 13 and the angular velocity sensor 14. Alternatively, a temperature correction function may be embedded in the acceleration sensor 13 and the angular velocity sensor 14.

The acceleration sensor 13 and the angular velocity sensor 14 may output analog signals. In this case, the control unit 11 may perform A/D (analog/digital) conversion on each of an output signal of the acceleration sensor 13 and an output signal of the angular velocity sensor 14, generate measurement data (acceleration data and angular velocity data), and generate packet data for communication using the measurement data.

The communication unit 12 performs, for example, a process of transmitting the packet data received from the control unit 11 to the motion analysis device 20 or a process of receiving control commands from the motion analysis device 20 and transmitting the control commands to the control unit 11. The control unit 11 performs various processes according to the control commands.

The motion analysis device 20 includes a control unit 21, a communication unit 22, an operation unit 23, a storage unit 24, a display unit 25, and a sound output unit 26.

The communication unit 22 performs, for example, a process of receiving the packet data transmitted from the sensor unit 10 and transmitting the packet data to the control unit 21 or a process of transmitting a control command from the control unit 21 to the sensor unit 10.

The operation unit 23 performs a process of acquiring operation data from the user and transmitting the operation data to the control unit 21. The operation unit 23 may be, for example, a touch panel type display, a button, a key, or a microphone.

The storage unit 24 is configured of, for example, any of various IC memories such as a read-only memory (ROM), a flash ROM, and a random access memory (RAM) or a recording medium such as a hard disk or a memory card.

The storage unit 24 stores, for example, programs used for the control unit 21 to perform various calculation processes or control processes, or various program or data used for the control unit 21 to realize application functions. In particular, in the embodiment, the storage unit 24 stores a motion analysis program which is read by the control unit 21 to perform a motion analysis process. The motion analysis program may be stored in advance in a nonvolatile recording medium. Alternatively, the motion analysis program may be received from a server via a network by the control unit 21 and may be stored in the storage unit 24.

In the embodiment, the storage unit 24 stores body information of the user 2, club specification information indicating the specification of the golf club 3, and sensor-mounted position information. For example, when the user 2 operates the operation unit 23 to input the body information such as a height, a weight, and a sex, the input body information is stored as body information in the storage unit 24. For example, the user 2 operates the operation unit 23 to input a model number of the golf club 3 (or selects the model number from a model number list) to be used and sets club specification information regarding the input model number as the specification information among pieces of specification information for each model number (for example, information regarding the length of the shaft, the position of the center of gravity, a lie angle, a face angle, a loft angle, and the like) stored in advance in the storage unit 24. For example, when the user 2 operates the operation unit 23 to input a distance between the position at which the sensor unit 10 is mounted and the grip end of the golf club 3, information regarding the input distance is stored as the sensor-mounted position information in the storage unit 24. Alternatively, by mounting the sensor unit 10 at a decided predetermined position (for example, a distance of 20 cm from the grip end), information regarding the predetermined position may be stored in advance as the sensor-mounted position information.

The storage unit 24 is used as a work area of the control unit 21 and temporarily stores, for example, data input from the operation unit 23 and calculation results performed according to various programs by the control unit 21. The storage unit 24 may store data necessarily stored for a long time among the data generated through the processes of the control unit 21.

The display unit 25 displays a processing result of the control unit 21 as text, a graph, a table, animations, or another image. The display unit 25 may be, for example, a cathode ray tube (CRT) display, a liquid crystal display (LCD), an electrophoretic display (EPD), a display using an organic light-emitting diode (OLED), a touch panel type display, or a head-mounted display (HMD). The functions of the operation unit 23 and the display unit 25 may be realized by one touch panel type display.

The sound output unit 26 outputs a processing result of the control unit 21 as audio such as a sound or a buzzer tone. The sound output unit 26 may be, for example, a speaker or a buzzer.

The control unit 21 performs a process of transmitting a control command to the sensor unit 10, various calculation processes on data received from the sensor unit 10 via the communication unit 22, and other various control processes according to various programs. In particular, in the embodiment, the control unit 21 executes a motion analysis program to function as a sensor information acquisition unit 210, a first imaginary plane specifying unit (which corresponds to a first specifying unit according to the invention) 211, a second imaginary plane specifying unit (which corresponds to a second specifying unit according to the invention) 212, an imaginary plane adjustment unit (which correspond to an adjustment unit according to the invention) 213, a motion analysis unit 214, an image generation unit 215, and an output processing unit 216. The first and second specifying units may be realized by separate calculation units or may be realized by the same calculation unit.

The control unit 21 may be realized, for example, by a computer that includes a central processing unit (CPU) which is a calculation device, a random access memory (RAM) which is a volatile storage device, a ROM which is a non-volatile storage device, an interface (I/F) circuit connecting the control unit 21 to the other units, a bus mutually connecting these units and the like. The computer may include various dedicated processing circuits such as image processing circuits. The control unit 21 may also be realized by an application specific integrated circuit (ASIC) or the like.

The sensor information acquisition unit 210 receives the packet data received from the sensor unit 10 by the communication unit 22 and acquires the time information and the measurement data from the received packet data. The sensor information acquisition unit 210 stores the acquired time information and measurement data in the storage unit 24 in association therewith.

The first imaginary plane specifying unit 211 performs a process of specifying the first line segment 51 in the major axis direction of the shaft of the golf club 3 at the time of stopping of the user, using the measurement data output by the sensor unit 10. Further, the first imaginary plane specifying unit 211 performs a process of specifying the shaft plane (first imaginary plane) 30 (see FIG. 2) including the first line segment 51 and the third line segment 52 indicating the hitting target direction.

The first imaginary plane specifying unit 211 may calculate the coordinates of the position 62 of the grip end of the golf club 3 using the measurement data output by the sensor unit 10 and specify the first line segment 51 based on the coordinates of the position 62 of the grip end. For example, the first imaginary plane specifying unit 211 may calculate an inclination angle (an inclination relative to the horizontal plane (the XY plane) or the vertical plane (the XZ plane)) of the shaft of the golf club 3, using the acceleration data measured by the acceleration sensor 13 at the time of stopping of the user 2 (the time of the address) and specify the first line segment 51 using the calculated inclination angle and information regarding the length of the shaft included in the club specification information.

The first imaginary plane specifying unit 211 may calculate the width of the shaft plane 30 using the length of an arm of the user 2 based on the body information and the length of the first line segment 51.

The second imaginary plane specifying unit 212 performs a process of specifying the second line segment 53 forming a predetermined angle relative to the first line segment 51 specified by the first imaginary plane specifying unit 211, using the hitting target direction (the third line segment 52) as the rotation axis. Further, the second imaginary plane specifying unit 212 performs a process of specifying the Hogan's plane (second imaginary plane) 40 (see FIG. 2) including the second line segment 53 and the third line segment 52.

For example, the second imaginary plane specifying unit 212 performs a process of estimating the predetermined position 63 between the head and the chest of the user 2 at the time of stopping of the user 2 (for example, on a line segment connecting both shoulders to one another) using the body information and the measurement data output by the sensor unit 10 and specifying the second line segment 53 connecting the estimated predetermined position 63 to the position 62 of the head (blow portion) of the golf club 3. The second imaginary plane specifying unit 212 performs a process of specifying the Hogan's plane 40 including the second line segment 53 and the third line segment 52.

The second imaginary plane specifying unit 212 may estimate the predetermined position 63 using the coordinates of the position 62 of the grip end calculated by the first imaginary plane specifying unit 211 and the length of the arm of the user 2 based on the body information. Alternatively, the second imaginary plane specifying unit 212 may calculate the coordinates of the position 62 of the grip end of the golf club 3 using the measurement data output by the sensor unit 10. In this case, the first imaginary plane specifying unit 211 may specify the shaft plane 30 using the coordinates of the position 62 of the grip end calculated by the second imaginary plane specifying unit 212.

The second imaginary plane specifying unit 212 may calculate the width of the Hogan's plane 40 using the length of the arm of the user 2 based on the body information and the length of the first line segment 51.

The imaginary plane adjustment unit 213 adjusts an angle of the first line segment 51 (an angle of the shaft plane) serving as the first axis and an angle of the second line segment 53 (an angle of the Hogan's plane) serving as the second axis according to the predetermined condition.

For example, the imaginary plane adjustment unit 213 receives a designation of the type of swing (for example, straight, hook, or slice) as the predetermined condition via the operation unit 23 from the user 2 and increases or decreases the angle of the first line segment 51 and the angle of the second line segment 53 relative to the horizontal plane according to the designated type of swing. In the embodiment, the imaginary plane adjustment unit 213 increases or decreases the angle of the first line segment 51 and the angle of the second line segment 53 while constantly maintaining a predetermined angle θ formed by the second line segment 53 and the angle of the first line segment 51. That is, the imaginary plane adjustment unit 213 rotates the V zone clockwise or counterclockwise using the hitting target direction (the third line segment 52) as a rotation axis.

In general, there are known tendencies in which straight-based hitting is realized when a trajectory of the golf club at the time of a downswing enters the V zone, slice-based hitting is realized when the trajectory is deviated from the V zone to the side of the Hogan's plane, and hook-based hitting is realized when the trajectory is deviated from the V zone to the side of the shaft plane. However, depending on a golfer, for example, a case in which a slice-based swing is performed can be considered to be a good state of a way. Accordingly, when a display position of the V zone can be adjusted so that the trajectory of a downswing enters the V zone in the good state of the way, it is possible to estimate goodness and badness of the swing simply in consideration of a type of swing of a golfer. Accordingly, in the embodiment, adjusting the position of the V zone is designed to be performed, as described above.

For example, the imaginary plane adjustment unit 213 receives a designation of a skill level (for example, a beginning course, an intermediate course, and an advanced course) as the predetermined condition via the operation unit 23 from the user 2, and then decreases the angle of the first line segment 51 and increases the angle of the second line segment 53 (the first line segment 51 and the second line segment 53 are kept away from one another) or increases the angle of the first line segment 51 and the decreases the angle of the second line segment 53 (the first line segment 51 and the second line segment 53 are kept close to each other) according to the designated skill level. That is, the imaginary plane adjustment unit 213 increases or decreases the predetermined angle θ formed by the second line segment 53 and the angle of the first line segment 51, using the hitting target direction (the third line segment 52) as the rotation axis.

In general, as the skill level of golf is lower, a trajectory of a golf club at the time of a downswing does not enter the V zone in many swings and the trajectory has an irregular tendency, and thus the swing is not stable. However, in the case of a beginner, when the area of the V zone specified based on the inclination or the like of the club is set as a criterion, as described above, for example, most of the swings are estimated to be bad. Thus, it is difficult to assess whether the swing is improved. In contrast, in the case of an advanced learner, when the area of the V zone specified is set as the criterion, as described above, for example, most of the swings are estimated to be good. Thus, it is difficult to assess whether the swing becomes stable or is further improved. Accordingly, when the area of the V zone can be adjusted in these cases, it is possible to estimate stability or improvement in the swing more accurately. Accordingly, in the embodiment, the area of the V zone described above can be designed to be adjusted.

The motion analysis unit 214 performs a process of analyzing a swing exercise of the user 2 using the measurement data output by the sensor unit 10. Specifically, the motion analysis unit 214 first calculates an offset amount included in the measurement data using the measurement data (the acceleration data and the angular velocity data) at the time of stopping of the user 2 (the time of the address), which is stored in the storage unit 24. Next, the motion analysis unit 214 subtracts the offset amount from the measurement data after start of a swing, which is stored in the storage unit 24 to correct a bias and calculates the position and posture of the sensor unit 10 during a swing motion of the user 2 using the measurement data in which the bias is corrected.

For example, the motion analysis unit 214 calculates the position (initial position) of the sensor unit 10 at the time of stopping of the user 2 (the time of the address) in the XYZ coordinate system (global coordinate system), using the acceleration data measured by the acceleration sensor 13, the club specification information, and the sensor-mounted position information, integrates the subsequent acceleration data, and chronologically calculates a change in the position of the sensor unit 10 from the initial position. Since the user 2 stops at a predetermined address posture, the X coordinate of the initial position of the sensor unit 10 is 0. Further, the y axis of the sensor unit 10 is identical to the major axis direction of the shaft of the golf club 3, and the acceleration sensor 13 measures only the gravity acceleration at the time of stopping of the user 2. Therefore, the motion analysis unit 214 can calculate an inclination angle of the shaft (an inclination relative to the horizontal plane (the XY plane) or the vertical plane (the XZ plane)), using y-axis acceleration data. Then, the motion analysis unit 214 can calculate the Y and Z coordinates of the initial position of the sensor unit 10 using the inclination angle of the shaft, the club specification information (the length of the shaft), and the sensor-mounted position information (the distance from the grip end) and specify the initial position of the sensor unit 10. Alternatively, the motion analysis unit 214 may calculate the coordinates of the initial position of the sensor unit 10 using the coordinates of the position 62 of the grip end of the golf club 3 calculated by the first imaginary plane specifying unit 211 or the second imaginary plane specifying unit 212 and the sensor-mounted position information (the distance from the grip end).

The motion analysis unit 214 calculates the posture (initial posture) of the sensor unit 10 at the time of stopping of the user 2 (the time of the address) in the XYZ coordinate system (global coordinate system), using the acceleration data measured by the acceleration sensor 13, performs rotation calculation using the angular velocity data measured subsequently by the angular velocity sensor 14, and chronologically calculates a change in the posture from the initial posture of the sensor unit 10. The posture of the sensor unit 10 can be expressed by, for example, rotation angles (a roll angle, a pitch angle, and a yaw angle) around the X axis, the Y axis, and the Z axis, Eulerian angles, quaternions, or the like. At the time of stopping of the user 2, the acceleration sensor 13 measures only the gravity acceleration. Therefore, the motion analysis unit 214 can specify an angle formed between of each of the x axis, y axis, and z axes of the sensor unit 10 and a gravity direction using triaxial acceleration data. Since the user 2 stops at the predetermined address posture, the y axis of the sensor unit 10 is present on the YZ plane at the time of stopping of the user 2. The motion analysis unit 214 can specify the initial posture of the sensor unit 10.

The control unit 11 of the sensor unit 10 may calculate the offset amount of the measurement data and correct the bias of the measurement data or a bias correction function may be embedded in the acceleration sensor 13 and the angular velocity sensor 14. In this case, it is not necessary to correct the bias of the measurement data by the motion analysis unit 214.

The motion analysis unit 214 defines a motion analysis model (a double pendulum model or the like) in consideration of the body information (the height (length of the arm) of the user 2), the club specification information (the length or the position of the center of the shaft), the sensor-mounted position information (the distance from the grip end), features (rigid body and the like) of the golf club 3, and features of a human body (for example, a joint bending direction is decided), and then calculate a trajectory of the golf club 3 at a swing of the user 2 using the motion analysis model and the information regarding the position and posture of the sensor unit 10.

The motion analysis unit 214 detects a series of motions (also referred to as a “rhythm”) from start to end of a swing of the user 2, for example, start of a swing, a backswing, a top, a downswing, an impact, follow-through, and end of the swing, using time information and the measurement data stored in the storage unit 24. For example, the motion analysis unit 214 calculates a composite value of the measurement data (the acceleration data or the angular velocity data) output by the sensor unit 10 and specifies a timing (time) of an impact by the user 2 based on the composite value.

Using the motion analysis model and information regarding the position and posture of the sensor unit 10, the motion analysis unit 214 may generate a rhythm of a swing from a backswing to follow-through, a head speed, an incident angle (club pass) or a face angle at the time of hitting, shaft rotation (a change amount of face angle during a swing), information regarding a deceleration rate or the like of the golf club 3, or information regarding a variation in each piece of information when the user 2 performs the swing a plurality of times.

The image generation unit 215 performs a process of generating image data corresponding to an image of a motion analysis result displayed on the display unit 25. In particular, in the embodiment, the image generation unit 215 generates image data including the shaft plane 30 specified by first imaginary plane specifying unit 211, the Hogan's plane 40 specified by the second imaginary plane specifying unit 212, and the trajectory of the golf club 3 at a swing (in particular, a downswing) of the user 2, which is calculated by the motion analysis unit 214. For example, the image generation unit 215 generates polygon data of the shaft plane 30 having the four vertexes T1, T2, S1, and S2 illustrated in FIG. 2 based on information regarding the coordinates of T1, T2, S1, and S2 and generates polygon data of the Hogan's plane 40 having the four vertexes T1, T2, H1, and H2 based on information regarding the coordinates of T1, T2, H1, and H2. The image generation unit 215 generates curved-line data indicating the trajectory of the golf club 3 at the time of a downswing of the user 2. Then, the image generation unit 215 generates image data including the polygon data of the shaft plane 30, the polygon data of the Hogan's plane 40, and the curved-line data indicating the trajectory of the golf club 3.

The first imaginary plane specifying unit 211, the second imaginary plane specifying unit 212, the imaginary plane adjustment unit 213, the motion analysis unit 214, and the image generation unit 215 also perform a process of storing various kinds of calculated information in the storage unit 24.

The output processing unit 216 performs a process of causing the display unit 25 to display various images (including not only an image corresponding to the image data generated by the image generation unit 215 but also text or signs). For example, the output processing unit 216 causes the display unit 25 to display the image corresponding to the image data generated by the image generation unit 215 automatically or according to an input operation of the user 2 after a swing motion of the user 2 ends. Alternatively, the sensor unit 10 may include a display unit, the output processing unit 216 may transmit the image data to the sensor unit 10 via the communication unit 22, and various images may be displayed on the display unit of the sensor unit 10.

The output processing unit 216 performs a process of causing the sound output unit 26 to output various kinds of audio (also including sound or buzzer tone). For example, the output processing unit 216 reads various kinds of information stored in the storage unit 24 and causes the sound output unit 26 to output audio or sound for motion analysis automatically or at the time of performing a predetermined input operation after a swing motion of the user 2 ends. Alternatively, the sensor unit 10 may include an sound output unit, the output processing unit 216 may transmit various kinds of audio data or sound data to the sensor unit 10 via the communication unit 22, and the sound output unit of the sensor unit 10 may be caused to output the various kinds of audio or sound.

The motion analysis device 20 or the sensor unit 10 may include a vibration mechanism and various kinds of information may be converted into vibration information by the vibration mechanism to be presented to the user 2.

FIG. 4 is a flowchart illustrating an example of an motion analysis process. The control unit 21 executes a motion analysis program stored in the storage unit 24 to perform the motion analysis process in the procedure of the flowchart illustrated in FIG. 4.

First, the sensor information acquisition unit 210 acquires the measurement data of the sensor unit 10 (step S10). When the control unit 21 acquires the first measurement data in a swing motion (also including a stopping motion) of the user 2, the control unit 21 may perform processes subsequent to step S20 in real time. Alternatively, after the control unit 21 acquires some or all of the series of measurement data in the swing motion of the user 2 from the sensor unit 10, the control unit 21 may perform the processes subsequent to step S20.

Next, the motion analysis unit 214 detects a stopping motion (address motion) of the user 2 using the measurement data acquired from the sensor unit 10 (step S20). When the control unit 21 performs the process in real time and detects the stopping motion (address motion), for example, the control unit 21 outputs a predetermined image or audio. Alternatively, for example, the sensor unit 10 may include a light-emitting unit such as a light emitting diode (LED) and blinks the light-emitting unit to notify the user 2 that the stopped state is detected so that the user 2 confirms the notification and subsequently starts a swing.

Next, the first imaginary plane specifying unit 211 specifies the shaft plane 30 (the first imaginary plane) using the measurement data (the measurement data in the stopping motion (address motion) of the user 2) acquired from the sensor unit 10 and the club specification information (step S30).

Next, the second imaginary plane specifying unit 212 specifies the Hogan's plane 40 (the second imaginary plane) using the measurement data (the measurement data in the stopping motion (address motion) of the user 2) acquired from the sensor unit 10 and the body information (step S40).

Next, the motion analysis unit 214 calculates the initial position and the initial posture of the sensor unit 10 using the measurement data (the measurement data in the stopping motion (address motion) of the user 2) acquired from the sensor unit 10 (step S50).

Next, the motion analysis unit 214 detects a series of motions (rhythm) from the start of the swing to the end of the swing using the measurement data acquired from the sensor unit 10 (step S60).

The motion analysis unit 214 calculates the position and posture of the sensor unit 10 during the swing motion of the user 2 concurrently with the process of step S60 (step S70).

Next, the motion analysis unit 214 calculates the trajectory of the golf club 3 during the swing motion of the user 2 using the rhythm detected in step S60 and the position and posture of the sensor unit 10 calculated in step S70 (step S80).

Next, the imaginary plane adjustment unit 213 adjusts the angle (the angle of the shaft plane) of the first line segment 51 serving as the first axis and the angle (the angle of the Hogan's plane) of the second line segment 53 serving as the second axis, that is, the V zone, according to the setting (the predetermined condition) (step S90).

Next, the image generation unit 215 generates the image data including the shaft plane specified in step S30 and the Hogan's plane specified in step S40 or the shaft plane and the Hogan's plane adjusted in step S90, and the trajectory of the golf club calculated in step S80 during the swing motion, and then the output processing unit 216 causes the display unit 25 to display the image data (step S100). Then, the control unit 21 ends the processes of the flowchart illustrated in FIG. 4.

In the flowchart of FIG. 4, the sequence of the processes may be appropriately changed within a possible range.

Next, an example of the process (the process of step S30 in FIG. 4) of specifying the shaft plane (the first imaginary plane) will be described in detail.

As illustrated in FIG. 2, the first imaginary plane specifying unit 211 first calculates the coordinates (0, G_(Y), G_(Z)) of the position 62 of the grip end based on the acceleration data at the time of the stopping measured by the sensor unit 10 and the club specification information by using the position 61 of the head of the golf club 3 as the origin O (0, 0, 0) of the XYZ coordinate system (global coordinate system). FIG. 5 is a plan view illustrating the golf club 3 and the sensor unit 10 at the time of stopping of the user 2 (the time of the address) when viewed from the negative side of the X axis. In FIG. 5, the position 61 of the head of the golf club 3 is the origin O (0, 0, 0) and the coordinates of the position 62 of the grip end are (0, G_(Y), G_(Z)). Since the gravity acceleration G is applied to the sensor unit 10 at the time of stopping of the user 2, a relation between the y axis acceleration y(0) and an inclination angle (an angle formed by the major axis of the shaft and the horizontal plane (XY plane)) α of the shaft of the golf club 3 is expressed in equation (1).

y(0)=G·sin α  (1)

Accordingly, when L₁ is the length of the shaft of the golf club 3 included in the club specification information, G_(Y) and G_(Z) are calculated using the length L₁ and the inclination angle α of the shaft in equations (2) and (3), respectively.

G _(Y) =L ₁·cos α  (2)

G _(Z) =L ₁·sin α  (3)

Next, the first imaginary plane specifying unit 211 multiplies the coordinates (0, G_(Y), G_(Z)) of the position 62 of the grip end of the golf club 3 by a scale factor S to calculate the coordinates (0, S_(Y), S_(Z)) of a midpoint S3 of the vertexes S1 and S2 of the shaft plane 30. That is, S_(Y) and S_(Z) are calculated using equations (4) and (5).

S _(Y) =G _(Y) ·S  (4)

S _(Z) =G _(Z) ·S  (5)

FIG. 6 is a diagram illustrating a cross section obtained by cutting the shaft plane 30 in FIG. 2 along the YZ plane when viewed from the negative side of the X axis. The length (the width of the shaft plane 30 in a direction perpendicular to the X axis) of a line segment connecting the origin O to the midpoint S3 of the vertexes S1 and S2 is S times the length L₁ of the first line segment 51. The scale vector S is set to a value so that the trajectory of the golf club 3 during the swing motion of the user 2 falls within the shaft plane 30. For example, when L₂ is the length of an arm of the user 2, the scale factor S may be set as in equation (6) so that a width S×L₁ in the direction perpendicular to the X axis of the shaft plane 30 is twice a sum of the length L₁ of the shaft and the length L₂ of the arm.

$\begin{matrix} {S = \frac{2 \cdot \left( {L_{1} + L_{2}} \right)}{L_{1}}} & (6) \end{matrix}$

The length L₂ of the arm of the user 2 has correlation with a height L₀ of the user 2. For example, based on statistical information, a correlation equation as in equation (7) is expressed when the user 2 is male, and a correlation equation as in equation (8) is expressed when the user 2 is female.

L ₂=0.41×L ₀−45.5 [mm]  (7)

L ₂=0.46×L ₀−126.9 [mm]  (8)

Accordingly, the length L₂ of the arm of the user is calculated by equation (7) or (8) using the height L₀ and sex of the user 2 included in the body information.

Next, the first imaginary plane specifying unit 211 calculates the coordinates (−TL/2, 0, 0) of the vertex T1, the coordinates (TL/2, 0, 0) of the vertex T2, the coordinates (−TL/2, S_(Y), S_(Z)) of the vertex S1, and the coordinates (TL/2, S_(Y), S_(Z)) of the S2 of the shaft plane 30 using the coordinates (0, S_(Y), S_(Z)) of the midpoint S3 calculated as described above and the width (the length of the third line segment 52) TL of the shaft plane 30 in the X axis direction. The width TL in the X axis direction is set to a value so that the trajectory of the golf club 3 during the swing motion of the user 2 falls within the shaft plane 30. For example, the width TL in the X axis direction may be set to be the same as the width S×L₁ in the direction perpendicular to the X axis, that is, twice the sum of the length L₁ of the shaft and the length L₂ of the arm.

The shaft plane 30 is specified based on the coordinates of the four vertexes T1, T2, S1, and S2 calculated in this way.

Next, an example of the process (the process of step S40 in FIG. 4) of specifying the Hogan's plane (the second imaginary plane) will be described in detail.

First, the second imaginary plane specifying unit 212 estimates the predetermined position 63 on the line segment connecting both shoulders of the user 2 to one another to calculate the coordinates (A_(X), A_(Y), A_(Z)), using the coordinates (0, G_(Y), G_(Z)) of the position 62 of the grip end of the golf club 3 calculated as described above and the body information of the user 2.

FIG. 7 is a diagram illustrating a cross section obtained by cutting the Hogan's plane 40 in FIG. 2 along the YZ plane when viewed from the negative side of the X axis. In FIG. 7, the midpoint of the line segment connecting both shoulders of the user 2 to one another is set as the predetermined position 63, and the predetermined position 63 is present on the YZ plane. Accordingly, the X coordinate A_(X) of the predetermined position 63 is 0. Then, the second imaginary plane specifying unit 212 estimates that a position obtained by moving the position 62 of the grip end of the golf club 3 by the length L₂ of the arm of the user 2 in the positive direction of the Z axis is the predetermined position 63. Accordingly, the Y coordinate A_(Y) of the predetermined position 63 is the same as the Y coordinate G_(Y) of the position 62 of the grip end, and the Z coordinate A_(Z) of the predetermined position 63 is calculated as a sum of the Z coordinate G_(Z) of the position 62 of the grip end and the length L₂ of the arm of the user 2, as in equation (9).

A _(Z) =G _(Z) +L ₂  (9)

The length L₂ of the arm of the user is calculated in equation (7) or (8) using the height L₀ and sex of the user 2 included in the body information.

Next, the second imaginary plane specifying unit 212 multiples the Y coordinate A_(Y) and the Z coordinate A_(Z) of the predetermined position 63 by a scale factor H to calculate the coordinates (0, H_(Y), H_(Z)) of a midpoint H3 of the vertexes H1 and H2 of the Hogan's plane 40. That is, H_(Y) and H_(Z) are calculated using equations (10) and (11).

H _(Y) =A _(Y) ·H  (10)

H _(Z) =A _(Z) ·H  (11)

As illustrated in FIG. 7, a length (a width of the Hogan's plane 40 in a direction perpendicular to the X axis) of a line segment connecting the origin O to the midpoint H3 of the vertexes H1 and H2 is H times the length L₃ of the second line segment 53. The scale factor H is set to a value so that the trajectory of the golf club 3 during the swing motion of the user 2 falls within the Hogan's plane 40. For example, the Hogan's plane 40 may have the same shape and size as the shaft plane 30. In this case, since a width H×L₃ of the Hogan's plane 40 in the direction perpendicular to the X axis is identical to the width S×L₁ of the shaft plane 30 in the direction perpendicular to the X axis and is twice the sum of the length L₁ of the shaft of the golf club 3 and the length L₂ of the arm of the user 2, the scale factor H may be set as in equation (12).

$\begin{matrix} {H = \frac{2 \cdot \left( {L_{1} + L_{2}} \right)}{L_{3}}} & (12) \end{matrix}$

The length L₃ of the second line segment 53 is calculated from equation (13) using the Y coordinate A_(Y) and the Z coordinate A_(Z) of the predetermined position 63.

L ₃=√{square root over (A _(Y) ² +A _(Z) ²)}  (13)

Next, the second imaginary plane specifying unit 212 calculates the coordinates (−TL/2, 0, 0) of the vertex T1, the coordinates (TL/2, 0, 0) of the vertex T2, the coordinates (−TL/2, H_(Y), H_(Z)) of the vertex H1, and the coordinates (TL/2, H_(Y), H_(Z)) of the H2 of the Hogan's plane 40 using the coordinates (0, H_(Y), H_(Z)) of the midpoint H3 calculated as described above and the width (the length of the third line segment 52) TL of the Hogan's plane 40 in the X axis direction. The width TL in the X axis direction is set to a value so that the trajectory of the golf club 3 during the swing motion of the user 2 falls within the Hogan's plane 40. In the embodiment, for example, the width TL Hogan's plane 40 in the X axis direction may be set to be the same as the width of the shaft plane 30 in the X axis direction, and thus may be set to be twice the sum of the length L₁ of the shaft and the length L₂ of the arm, as described above.

The Hogan's plane 40 is specified based on the coordinates of the four vertexes T1, T2, H1, and H2 calculated in this way.

Next, an example of the process (the process of step S60 in FIG. 4) of detecting a series of motions (rhythm) from the start of the swing to the end of the swing of the user 2 will be described in detail.

The motion analysis unit 214 detects a series of motions (rhythm) from the start of the swing to the end of the swing, for example, the start of the swing, a backswing, a top, a downswing, an impact, follow-through, and the end of the swing, using the measurement data acquired from the sensor unit 10. A specific rhythm detection procedure is not particularly limited. For example, the following procedure can be adopted.

First, the motion analysis unit 214 calculates a sum (referred to as a composite value or a norm) of the magnitudes of the angular velocities around the axes at each time t using the acquired angular velocity data of each time t. The motion analysis unit 214 may integrate the norm of the angular velocities at each time t by time.

Here, a case of a graph in which angular velocities around three axes (x, y, and z axes) are shown, for example, in FIG. 8 (which is a diagram illustrating examples of angular velocities output from the sensor unit) will be considered. In FIG. 8, the horizontal axis represents a time (msec) and the vertical axis represents an angular velocity (dps). The norm of the angular velocities is shown in the graph illustrated in, for example, FIG. 9 (which is a diagram illustrating an example of the norm of the angular velocities). In FIG. 9, the horizontal axis represents a time (msec) and the vertical axis represents the norm of the angular velocities. A differential value of the norm of the angular velocities is shown in a graph illustrated in, for example, FIG. 10 (which is a diagram illustrating an example of the differential value of the norm of the angular velocities). In FIG. 10, the horizontal axis represents a time (msec) and the vertical axis represents the differential value of the norm of the vertical angular. FIGS. 8 to 10 are exemplified to facilitate understanding of the embodiment and do not show accurate values.

The motion analysis unit 214 detects a timing of an impact in the swing using the calculated norm of the angular velocities. For example, the motion analysis unit 214 detects a timing at which the norm of the angular velocities is the maximum as the timing of the impact (T5 in FIG. 9). Alternatively, for example, the motion analysis unit 214 may detect a former timing between timings at which the value of the differential of the calculated norm of the angular velocities is the maximum and the minimum as the timing of the impact (T5 in FIG. 10).

For example, the motion analysis unit 214 detects a timing at which the calculated norm of the angular velocities is the minimum before the impact as a timing of a top of the swing (T3 in FIG. 9). For example, the motion analysis unit 214 specifies a period in which the norm of the angular velocities is continuously equal to or less than a first threshold value before the impact, as a top period (which is an accumulation period at the top) (T2 to T4 in FIG. 9).

For example, the motion analysis unit 214 detects a timing at which the norm of the angular velocities is equal to or less than a second threshold value before the top, as a timing of the start of the swing (T1 in FIG. 9).

For example, the motion analysis unit 214 detects a timing at which the norm of the angular velocities is the minimum after the impact, as a timing of the end (finish) of the swing (T7 in FIG. 9). For example, the motion analysis unit 214 may detect a timing at which the norm of the angular velocities is first equal to or less than the third threshold value after the impact, as the timing of the end (finish) of the swing. For example, the motion analysis unit 214 specifies a period in which the norm of the angular velocities is continuously equal to or less than a fourth threshold value after the timing of the impact and close to the timing of the impact, as a finish period (T6 to T8 in FIG. 9).

In this way, the motion analysis unit 214 can detect the rhythm of the swing. The motion analysis unit 214 can specify each period (for example, a backswing period from the start of the swing to the start of the top, a downswing period from the end of the top to the impact, and a follow-through period from the impact to the end of the swing) during the swing by detecting the rhythm.

Next, an example of the process (the process of step S100 in FIG. 4) of generating and displaying the image data indicating the V zone and the trajectory will be described in detail. Here, a case in which the V zone is not adjusted in step S90 of FIG. 4 will be described.

FIG. 11 is a diagram illustrating an example of a screen including the shaft plane and the Hogan's plane. FIG. 11 is a diagram in which the shaft plane and the Hogan's plane are projected to the YZ plane.

An image 500 includes polygon data 501 indicating the shaft plane 30, polygon data 502 indicating the Hogan's plane 40, and a curved line 503 indicating the trajectory of the golf club 3 at the time of a downswing of the user 2. In the image 500, a V zone which is a space between the polygon data 501 and the polygon data 502 can be recognized.

In FIG. 11, when the V zone is displayed, the V zone may not necessarily be displayed with the planes, but only the first line segment 51 (or a straight line along the first line segment 51) included in the shaft plane 30 and the second line segment 53 (or a straight line along the second line segment 53) included in the Hogan's plane 40 may be displayed. The image illustrated in FIG. 11 may be a 3-dimensional image of which a display angle (a viewpoint for viewing an image) can be changed according to an operation of the user 2.

Next, an example of the process (the process of step S90 in FIG. 4) of adjusting the V zone will be described in detail.

In the embodiment, the motion analysis device 20 receives setting of the adjusting of the V zone in advance from the user 2. For example, the imaginary plane adjustment unit 213 causes the display unit 25 to display a screen 600 illustrated in FIG. 12 (which is a diagram illustrating an example of a screen on which display setting of the V zone is performed) and receives an operation input on the screen 600 via the operation unit 23 from the user 2.

The screen 600 includes a type-of-swing field 610 for designating the type of swing, a skill level field 620 for designating the skill level, a center plane field 630 for designating display or non-display of a center plane, and a V zone field 640 for designating display or non-display of a reference V zone. In the example of FIG. 12, the type-of-swing field 610 includes three buttons so that anyone of three types of swings (straight, hook, and slice) can be designated. The skill level field 620 includes three buttons so that any one of three skill levels (beginning, intermediate, and advanced) can be designated.

The center plane is a plane that is formed by the third line segment 52 and a line segment bisecting a predetermined angle θ formed by the first line segment 51 and the second line segment 53 using the target direction (the third line segment 52) of the hitting as the rotation axis. In the example of FIG. 12, the center plane field 630 includes two buttons so that display or non-display of the center plane can be designated.

The reference V zone is a V zone (for example, a V zone of a professional golfer or a past V zone of the user 2) that is displayed for comparison reference apart from the V zone of the user 2 specified and displayed as above described. Information regarding the reference V zone (for example, data specifying the angle of the shaft plane and the angle of the Hogan's plane of the reference V zone) may be stored in, for example, the storage unit 24 or a storage device on a network. In the example of FIG. 12, the reference V zone field 640 includes two buttons so that display or non-display of the reference V zone can be designated. The reference V zone field 640 includes a button for setting an acquisition destination (for example, a URL or a file path) of the information regarding the reference V zone.

The description will be continued below with reference to FIGS. 13A to 16 assuming the initial setting in which the type of swing is “straight”, the skill level is “intermediate”, the center plane is “non-display”, and the reference V zone is “non-display”.

FIGS. 13A to 13C are diagrams illustrating examples of a procedure and a screen for adjusting the shaft plane and the Hogan's plane according to the type of swing.

When “straight” is set in the above-described type-of-swing field 610, the imaginary plane adjustment unit 213 does not adjust the V zone. Specifically, the imaginary plane adjustment unit 213 does not change the angle of the shaft plane 30 specified in step S30 and the angle of the Hogan's plane 40 specified in step S40. In FIG. 13A, the shaft plane 30 at the inclination angle α and the Hogan's plane 40 forming a predetermined angle θ relative to the shaft plane 30 are specified. The image generation unit 215 generates and displays the image 500 including the polygon data 501 of the shaft plane 30, the polygon data 502 of the Hogan's plane 40, and the curved line 503 (not illustrated) indicating the trajectory of the golf club 3.

When “slice” is set in the above-described type-of-swing field 610, the imaginary plane adjustment unit 213 performs adjustment by rotating the V zone clockwise. Specifically, the imaginary plane adjustment unit 213 specifies a shaft plane 30 a and a Hogan's plane 40 a after the adjustment by rotating the angle of the shaft plane 30 specified in step S30 and the angle of the Hogan's plane 40 specified in step S40 by an angle adjustment amount d in the Z axis direction, using the third line segment 52 as the rotation axis. In FIG. 13B, the shaft plane 30 a at an inclination angle α+d and the Hogan's plane 40 a forming the predetermined angle θ relative to the shaft plane 30 a are specified. The image generation unit 215 generates and displays the image 500 including polygon data 501 a of the shaft plane 30 a, polygon data 502 a of the Hogan's plane 40 a, and the curved line 503 (not illustrated) indicating the trajectory of the golf club 3.

When “hook” is set in the above-described type-of-swing field 610, the imaginary plane adjustment unit 213 performs adjustment by rotating the V zone counterclockwise. Specifically, the imaginary plane adjustment unit 213 specifies the shaft plane 30 a and the Hogan's plane 40 a after the adjustment by rotating the angle of the shaft plane 30 specified in step S30 and the angle of the Hogan's plane 40 specified in step S40 by the angle adjustment amount d in the Y axis direction, using the third line segment 52 as the rotation axis. In FIG. 13C, the shaft plane 30 a at an inclination angle α−d and the Hogan's plane 40 a forming the predetermined angle θ relative to the shaft plane 30 a are specified. The image generation unit 215 generates and displays the image 500 including the polygon data 501 a of the shaft plane 30 a, the polygon data 502 a of the Hogan's plane 40 a, and the curved line 503 (not illustrated) indicating the trajectory of the golf club 3.

Since the position of the V zone is adjusted according to the type of swing designated by the user 2 in the above-described manner, the swing can be estimated accurately according to the type of swing. For example, when a golfer performing a sliced-based swing usually sets the display setting of the V zone to “slice”, the trajectory of a downswing easily falls within the V zone, and thus goodness and the badness of a way or the goodness and the badness of a swing can be determined simply and accurately.

FIGS. 14A and 14B are diagrams illustrating examples of a procedure and a screen for adjusting shaft plane and the Hogan's plane according to a skill level.

When “intermediate” is set in the above-described skill level field 620, the imaginary plane adjustment unit 213 does not adjust the V zone. Since this case is the same as the case of FIG. 13A, the description thereof will be omitted.

When “beginning” is set in the above-described skill level field 620, the imaginary plane adjustment unit 213 performs adjustment so that the center angle of the V zone formed by the shaft plane 30 and the Hogan's plane 40 is large. Specifically, the imaginary plane adjustment unit 213 specifies the shaft plane 30 a after adjustment by rotating the angle of the shaft plane 30 specified in step S30 by an angle adjustment amount d in the Y axis direction, using the third line segment 52 as the rotation axis. The imaginary plane adjustment unit 213 specifies the Hogan's plane 40 a after adjustment by rotating the angle of the Hogan's plane 40 specified in step s40 by the angle adjustment amount d in the Z axis direction, using the third line segment 52 as the rotation axis. In FIG. 14A, the shaft plane 30 a at the inclination angle α−d and the Hogan's plane 40 a forming a predetermined angle θ+2d relative to the shaft plane 30 a are specified. The image generation unit 215 generates and displays the image 500 including the polygon data 501 a of the shaft plane 30 a, the polygon data 502 a of the Hogan's plane 40 a, and the curved line 503 (not illustrated) indicating the trajectory of the golf club 3.

When “advanced” is set in the above-described skill level field 620, the imaginary plane adjustment unit 213 performs adjustment so that the center angle of the V zone formed by the shaft plane 30 and the Hogan's plane 40 is small. Specifically, the imaginary plane adjustment unit 213 specifies the shaft plane 30 a after adjustment by rotating the angle of the shaft plane 30 specified in step S30 by the angle adjustment amount d in the Z axis direction, using the third line segment 52 as the rotation axis. The imaginary plane adjustment unit 213 specifies the Hogan's plane 40 a after adjustment by rotating the angle of the Hogan's plane 40 specified in step S40 by the angle adjustment amount d in the Y axis direction, using the third line segment 52 as the rotation axis. In FIG. 14B, the shaft plane 30 a at the inclination angle α+d and the Hogan's plane 40 a forming a predetermined angle θ−2d relative to the shaft plane 30 a are specified. The image generation unit 215 generates and displays the image 500 including the polygon data 501 a of the shaft plane 30 a, the polygon data 502 a of the Hogan's plane 40 a, and the curved line 503 (not illustrated) indicating the trajectory of the golf club 3.

The area of the V zone is adjusted according to the skill level designated by the user 2 in the above-described manner. That is, as the skill level is lower, the adjustment is performed so that the center angle of the V zone is larger. As the skill level is higher, the adjustment is performed so that the center angle of the V zone is smaller. Therefore, the swing can be estimated accurately according to the skill level. For example, when a beginning golfer sets the display setting of the V zone to “beginning”, the trajectory of a downswing easily falls within the V zone, and thus goodness and the badness of a way, the goodness and the badness of a swing, or the degree of improvement can be determined simply and accurately.

FIG. 15 is s diagram illustrating examples of a procedure and a screen for setting a center plane.

When “display” is set in the above-described center plane field 630, the imaginary plane adjustment unit 213 specifies the center plane. Specifically, the imaginary plane adjustment unit 213 specifies a middle inclination of the inclination of the shaft plane 30 specified in step S30 and the inclination of the Hogan's plane 40 specified in step S40 as an inclination of the center plane, using the third line segment 52 as the rotation axis. In FIG. 15, a center plane 50 at an inclination angle α+θ/2 is specified. The image generation unit 215 generates and displays the image 500 including the polygon data 501 of the shaft plane 30, the polygon data 502 of the Hogan's plane 40, polygon data 504 of the center plane 50, and the curved line 503 (not illustrated) indicating the trajectory of the golf club 3.

In the above-described manner, the center plane is displayed according to designation of the user 2. Referring to the center plane, the user 2 can simply determine to which side the trajectory of the swing is biased between the shaft plane and the Hogan's plane, for example.

FIG. 16 is a diagram illustrating example of a procedure and a screen for setting a reference V zone.

When “display” is set in the above-described reference V zone 640 and the acquisition destination of the information regarding the reference V zone is set, the imaginary plane adjustment unit 213 acquires the information regarding the reference V zone from the acquisition destination. The imaginary plane adjustment unit 213 specifies a shaft plane and a Hogan's plane forming the reference V zone based on the information regarding the acquired reference V zone. In FIG. 16, a shaft plane 30 b and a Hogan's plane 40 b forming the reference V zone are specified in addition to the shaft plane 30 specified in step S30 and the Hogan's plane 40 specified in step S40. The image generation unit 215 generates and displays the image 500 including the polygon data 501 of the shaft plane 30, the polygon data 502 of the Hogan's plane 40, polygon data 501 b of the shaft plane 30 b, polygon data 502 b of the Hogan's plane 40 b, and the curved line 503 (not illustrated) indicating the trajectory of the golf club 3.

In the above-described manner, the reference V zone is displayed according to designation of the user 2. The user 2 can estimate the address posture or improve the address posture by comparing the V zone of the user to the reference V zone.

The designation of the type of swing, the designation of the skill level, the designation of the display of the center plane, and the designation of the display of the reference V zone have been separately described in FIGS. 13A to 16, but the designation can also be performed by combining at least one thereof. For example, when the type of swing “slice” and the skill level “beginning” are designated, the imaginary plane adjustment unit 213 may rotate the V zone clockwise and enlarge the center angle. For example, when the type of swing “hook” and the skill level “advanced” are designated, the imaginary plane adjustment unit 213 may rotate the V zone counterclockwise and narrow the center angle. The center plane 50 may be specified based on the shaft plane 30 a and the Hogan's plane 40 a after the adjustment of the V zone.

The magnitude of the above-described adjustment amount d in FIGS. 13A to 14B may be able to be designated by the user 2. For example, when the type of swing is designated, the degrees of slice and hook may be able to be designated in a plurality of stages with reference to the straight on the screen 600 and the imaginary plane adjustment unit 213 may perform setting such that the adjustment amount d is larger as the designated degree of slice or hook is larger. For example, when the skill level is designated, a plurality of levels may be able to be designated at each of the higher and lower levels using the intermediate as a criterion on the screen 600 and the imaginary plane adjustment unit 213 may perform setting so that the adjustment amount d is larger as the skill is higher (or the skill is lower).

In the example of FIGS. 13A to 13C, the same adjustment amount d is used for the shaft plane 30 and the Hogan's plane 40, but the imaginary plane adjustment unit 213 may use different adjustment amounts (one of the adjustment amounts may be 0). Similarly, in the example of FIGS. 14A and 14B, the same adjustment amount d is used for the shaft plane 30 and the Hogan's plane 40, but the imaginary plane adjustment unit 213 may use different adjustment amounts (one of the adjustment amounts may be 0).

The imaginary plane adjustment unit 213 may decide the magnitude of the adjustment amount d according to the type of club (for example, a driver and a driver model number, an iron and an iron model number, and a putter) or specification information (for example, the length of the shaft, the position of the center of gravity, a lie angle, a face angle, and a loft angle) of the designated club. The imaginary plane adjustment unit 213 may decide the magnitude of the adjustment amount d according to designated body information (for example, the length of an arm and the height) regarding the user.

The embodiment of the invention has been described above. According to the embodiment, since the user can objectively recognize the address posture from the positions and inclinations of the shaft plane and the Hogan's plane, the size of the V zone, and the like, it is possible to estimate the goodness and badness of a swing more simply. Since the user can recognize the positional relation between the trajectory of the golf club and the shaft plane and the Hogan's plane at the time of a swing, it is possible to estimate the goodness and badness of a swing more accurately than in the related art.

According to the embodiment, by imposing the restriction that the user performs address so that the major axis of the shaft of the golf club is vertical to the target line, the motion analysis device can specify the third line segment indicating the target direction of the hitting using the measurement data of the sensor unit at the time of the address. Accordingly, the motion analysis device can appropriately specify the shaft plane in accordance with the direction of the third line segment.

According to the embodiment, since the predetermined position on the line segment connecting both shoulders of the user in the Hogan's plane is specified in consideration of the body information of the user, the shaft plane and the Hogan's plane can be specified using the measurement data of one sensor unit. It is possible to specify the Hogan's plan suitable for the body shape of the user more accurately than a case in which an imaginary plane obtained by rotating the shaft plane by a predetermined angle (for example, 30°) is specified as the Hogan's plane.

According to the embodiment, the position, the posture, or the like of they zone specified based on the address posture of the user is adjusted according to the type of swing. Accordingly, even when the estimation is desired to be performed in consideration of a swing tendency or the like according to the type of swing, it is possible to estimate the goodness and badness of a swing simply and accurately.

According to the embodiment, the position, the posture, the area, or the like of the V zone specified based on the address posture of the user is adjusted according to the skill level. Accordingly, even when the estimation is desired to be performed in consideration of a swing tendency or the like according to the skill level, it is possible to estimate the goodness and badness of a swing simply and accurately.

According to the embodiment, since the shaft plane and the Hogan's plane are specified using the sensor unit, it is not necessary to use a large-scale device such as a camera and restriction of a place where a swing is analyzed is small.

The invention is not limited to the above-described embodiments, but may be modified in various forms within the scope of the gist of the invention.

In the foregoing embodiments, the second imaginary plane specifying unit 212 specifies the second line segment 53 using the body information and the measurement data output by the sensor unit 10. However, a process of specifying the second line segment 53 connecting the positions 63 and 62 of the head (the blow portion) of the golf club 3 may be performed using the first line segment 51 specified by the first imaginary plane specifying unit 211 and the predetermined angle θ relative to the first line segment 51.

In the foregoing embodiments, the motion analysis device 20 specifies the shaft plane and the Hogan's plane using the measurement data of the sensor unit 10 mounted on the golf club 3 and calculates the trajectory of the golf club 3 during the swing. Besides, for example, the shaft plane and the Hogan's plane may be specified and the trajectory of the golf club 3 may be calculated using the measurement data of the sensor unit 10 mounted on an arm (wrist or the like) of the user 2 in the same method as that of the foregoing embodiment. Alternatively, the plurality of sensor units 10 may be mounted on parts such as the golf club 3 or the arms, shoulders, or the like of the user. Then, the shaft plane and the Hogan's plane may be specified and the trajectory of the golf club 3 may be calculated using the measurement data of each of the plurality of sensor units 10.

In the foregoing embodiments, the acceleration sensor 13 and the angular velocity sensor 14 are embedded in the sensor unit 10 to be integrated, but the acceleration sensor 13 and the angular velocity sensor 14 may not be integrated. Alternatively, the acceleration sensor 13 and the angular velocity sensor 14 may not be embedded in the sensor unit 10, but may be mounted directly on the golf club 3 or the user 2. In the foregoing embodiments, the sensor unit 10 and the motion analysis device 20 are separated, but the acceleration sensor 13 and the angular velocity sensor 14 may be integrated to be mounted on the golf club 3 or the user 2.

In the foregoing embodiments, the motion analysis device 20 calculates the Z coordinate A_(Z) of the predetermined position 63 on the line segment connecting both shoulders of the user 2 to one another as the sum of the Y coordinate G_(Y) of the position 62 of the grip end and the length L₂ of the arm of the user 2 as in equation (9), but another equation may be used. For example, the motion analysis device 20 may multiply L₂ by a coefficient K and adds G_(Y) to calculate A_(Z) as in A_(Z)=G_(Y)+K·L₂.

In the foregoing embodiments, the motion analysis system (the motion analysis device) analyzing a golf swing has been exemplified. However, the invention can be applied to an motion analysis system (motion analysis device) analyzing swings of various exercises of tennis, baseball, and the like.

The above-described embodiments and modification examples are merely examples and the invention is not limited thereto. For example, the embodiments and the modification examples can also be appropriately combined.

The configuration of the motion analysis system 1 illustrated in FIG. 3 is classified according to main processing content in order to facilitate understanding of the configuration of the motion analysis system 1. The invention is not limited by the method of classifying the constituent elements or the names of the constituent elements. The configuration of the motion analysis system 1 can be classified into further many constituent elements according to the processing content. One constituent element can be classified to perform more processes. The process of each constituent element may be performed by one piece of hardware or may be performed by a plurality of pieces of hardware. Charge of the processor function of each constituent element is not limited to the above description as long as the goal and advantage of the invention can be achieved. In the foregoing embodiment, the sensor unit 10 and the motion analysis device 20 have been described as separate units, but the function of the motion analysis device 20 may be mounted on the sensor unit 10.

Units of processes in the flowchart illustrated in FIG. 4 are divided according to main processing content in order to facilitate understanding of the process of the motion analysis device 20. The invention is not limited by a method of dividing the units of processes or the names of the units of processes. The process of the motion analysis device 20 can be divided in more units of processes according to the processing content. One unit of process can be divided to include more processes. The processing procedure of the foregoing flowchart is not limited to the example illustrated in the drawing.

The entire disclosure of Japanese Patent Application No. 2014-257261, filed Dec. 19, 2014 is expressly incorporated by reference herein. 

What is claimed is:
 1. A motion analysis device comprising: a first specifying unit that specifies a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of an inertial sensor; a second specifying unit that specifies a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and an adjustment unit that adjusts sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.
 2. The motion analysis device according to claim 1, wherein the predetermined condition is a type of swing of the user, and wherein the adjustment unit adjusts at least one of the angle of the first axis and the angle of the second axis according to the type of swing.
 3. The motion analysis device according to claim 2, wherein the type of swing is a slice or a hook, wherein when the type of swing is the slice, the adjustment unit increases at least the angle of the second axis, and wherein when the type of swing is the hook, the adjustment unit decreases at least the angle of the first axis.
 4. The motion analysis device according to claim 1, wherein the predetermined condition is a skill level of the user, and wherein the adjustment unit adjusts the predetermined angle between the first and second axes according to the skill level.
 5. The motion analysis device according to claim 4, wherein the adjustment unit increases the predetermined angle as the skill level is lower, and wherein the adjustment unit decreases the predetermined angle as the skill level is higher.
 6. The motion analysis device according to claim 1, wherein the first specifying unit calculates an angle of the shaft relative to the plane using an output of the inertial sensor at the address posture, and specifies the first axis using information regarding a length of the shaft and this angle.
 7. The motion analysis device according to claim 1, wherein when the hitting direction is a third axis, the first specifying unit specifies a first imaginary plane including the first and third axes and the second specifying unit specifies a second imaginary plane including the second and third axes.
 8. The motion analysis device according to claim 1, wherein the exercise tool includes a blow surface, and wherein the hitting direction is a direction perpendicular to the blow surface at the address posture.
 9. The motion analysis device according to claim 1, further comprising: an image generation unit that generates image data including the first and second axes.
 10. The motion analysis device according to claim 9, further comprising: a motion analysis unit that calculates a trajectory of the exercise tool based on a swing of the user, wherein the image generation unit generates image data including the first axis, the second axis, and the trajectory.
 11. A motion analysis system comprising: an inertial sensor; a first specifying unit that specifies a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of the inertial sensor; a second specifying unit that specifies a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and an adjustment unit that adjusts sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.
 12. The motion analysis system according to claim 11, wherein the predetermined condition is a type of swing of the user, and wherein the adjustment unit adjusts at least one of the angle of the first axis and the angle of the second axis according to the type of swing.
 13. The motion analysis system according to claim 12, wherein the type of swing is a slice or a hook, wherein when the type of swing is the slice, the adjustment unit increases at least the angle of the second axis, and wherein when the type of swing is the hook, the adjustment unit decreases at least the angle of the first axis.
 14. The motion analysis system according to claim 11, wherein the predetermined condition is a skill level of the user, and wherein the adjustment unit adjusts the predetermined angle between the first and second axes according to the skill level.
 15. An motion analysis method comprising: specifying a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of an inertial sensor; specifying a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and adjusting sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.
 16. The motion analysis method according to claim 15, wherein the predetermined condition is a type of swing of the user, and wherein in the adjusting of the sizes of the angles, at least one of the angle of the first axis and the angle of the second axis is adjusted according to the type of swing.
 17. The motion analysis method according to claim 16, wherein the type of swing is a slice or a hook, wherein when the type of swing is the slice, at least the angle of the second axis is increased in the adjusting of the sizes of the angles, and wherein when the type of swing is the hook, at least the angle of the first axis is decreased in the adjusting of the sizes of the angles.
 18. The motion analysis method according to claim 15, wherein the predetermined condition is a skill level of the user, and wherein in the adjusting of the sizes of the angles, the predetermined angle between the first and second axes is adjusted according to the skill level.
 19. A program causing a computer to perform: specifying a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of an inertial sensor; specifying a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and adjusting sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.
 20. A recording medium that records a program causing a computer to perform: specifying a first axis which lies in a longitudinal direction of a shaft of an exercise tool at an address posture of a user, using an output of an inertial sensor; specifying a second axis forming a predetermined angle along with the first axis, using a hitting direction as a rotation axis; and adjusting sizes of an angle of the first axis and an angle of the second axis relative to a plane according to a predetermined condition.
 21. A motion analysis device comprising: an adjustment unit that adjusts a size of a center angle of a V zone according to a predetermined condition.
 22. The motion analysis device according to claim 21, wherein the predetermined condition is a skill level of the user, and wherein the adjustment unit adjusts the center angle according to the skill level.
 23. The motion analysis device according to claim 22, wherein the adjustment unit increases the center angle as the skill level is lower, and wherein the adjustment unit decreases the center angle as the skill level is higher.
 24. The motion analysis device according to claim 21, wherein an exercise tool includes a blow surface, and wherein the hitting direction is a direction perpendicular to the blow surface at a address posture of a user.
 25. The motion analysis device according to claim 21, further comprising: an image generation unit that generates image data including the V zone.
 26. The motion analysis device according to claim 25, further comprising: a motion analysis unit that calculates a trajectory of an exercise tool based on a swing of the user, wherein the image generation unit generates image data including the V zone and the trajectory. 